The present invention relates to a movement control apparatus, printing apparatus, and movement control method and, more particularly, to control of the current position of a member to be driven by using an encoder having a scale equipped with a plurality of indices at a predetermined interval and a sensor which is attached to the member driven along the scale and detects an index.
Printers for printing desired information such as characters or images on a sheet-like printing medium such as a paper sheet or film are widely used as an information output apparatus for a word processor, personal computer, or a facsimile apparatus.
The printing method of the printer includes various methods. An ink-jet method has recently received a great deal of attention because it can perform non-contact printing on a printing medium such as a paper sheet, can easily print a full-color image, and is quiet. As an ink-jet arrangement, a serial printing method is generally widely used in terms of low cost and easy downsizing. In the serial printing method, a printing head for discharging ink in accordance with desired printing information is mounted on a carriage. Information is printed by reciprocally scanning the carriage in a direction perpendicular to the feed direction of a printing medium such as a paper sheet (main scanning).
In recent years, high-resolution serial printers have been available along with the development of the printing technique. In this high-resolution printer, the precision of position information in the main scanning direction greatly influences the printing quality.
As for the printer performance, demands have arisen for higher printing speed in addition to higher printing resolution. Higher-speed, higher-resolution printers have been commercially available year after year.
To increase the printing speed, the moving speed in the main scanning direction must be increased. As the speed increases, the precision of position information necessary for high-resolution printing degrades.
To prevent this, there are proposed many printers using so-called encoders in order to accurately acquire position information. This encoder outputs the index of the absolute position of a printing head-mounted carriage in the main scanning direction. The encoder is, e.g., an optical encoder.
A general optical encoder is constituted by fixing a reference (scale) having indices at a small interval in the main scanning direction to a printer main body. An index is read by a sensor on the carriage, and the moving position and speed of the carriage are detected by a sensor output signal. In general, the indices are printing position indices and are set as position information (space information) at a predetermined interval.
The index interval (position resolving power) desirably coincides with the actual printing resolution (printing interval). If the resolution becomes higher, as described above, a corresponding scale must be manufactured, and the sensitivity of the sensor for reading information from the scale must be increased, resulting in a high-cost encoder.
To decrease the encoder cost, a scale lower in resolving power than the actual printing resolution is adopted. Printing position information at higher resolution is generated by interpolation. The moving position of the carriage and driving of the printing head are controlled in accordance with the printing position information. In this case, only the range where the carriage moves at a constant speed is set as a printing region in order to ensure the precision of printing position information.
FIG. 4 is a graph showing the relationship between the carriage moving speed and the time. In the graph, the abscissa represents the time, and the ordinate represents the moving speed. As shown in this graph, the time required for the overall carriage movement is B, and the time during which the carriage moves at a constant speed is A. The time used for printing is only A out of the time B during which the carriage moves. The time (Bxe2x88x92A) (acceleration/deceleration time) is idle in terms of printing.
This greatly influences even the size of the printer main body. That is, a region for accelerating/decelerating the carriage is required in the main scanning direction in addition to the printing region. The printer width in the main scanning direction increases.
To shorten the printing time, the speed in the constant-speed region must be increased, and the time necessary for acceleration/deceleration must be shortened. In this case, the acceleration/deceleration curve becomes steep, and large kinetic energy must be applied to the carriage as a target to be moved.
Supplying large energy requires a high-strength driving mechanism such as a motor. Electric energy (electric power) consumed by the driving mechanism increases. As a result, the driving mechanism becomes bulky and expensive, which is disadvantageous in terms of power consumption.
This problem is not confined to a printing apparatus such as a printer. The same problem occurs even in other electronic devices having a movable portion which moves reciprocally, such as a scanner and copying machine.
It is the first object of the present invention to provide a movement control apparatus capable of controlling the current position of a member to be driven with high precision even during acceleration/deceleration.
It is the second object of the present invention to provide a printing apparatus capable of controlling the current position of a member to be driven with high precision even during acceleration/deceleration.
It is the third object of the present invention to provide a movement control method capable of controlling the current position of a member to be driven with high precision even during acceleration/deceleration.
The first object is attained by a movement control apparatus according to the first aspect of the present invention comprising a scale having a plurality of indices at a predetermined interval, a sensor which is attached to a member to be driven along the scale and detects the indices, prediction means for predicting, on the basis of an output waveform of the sensor, a time until a next index is detected, and position signal generation means for generating a signal concerning a current position of the member on the basis of the predicted time.
The second object is attained by a printing apparatus according to the second aspect of the present invention comprising a scale which is attached to a guide shaft and has a plurality of indices at a predetermined interval, a sensor which is attached to a carriage which supports a printing head to be driven along the guide shaft and detects the indices, prediction means for predicting, on the basis of an output waveform of the sensor, a time until a next index is detected, and position signal generation means for generating a signal concerning a current position of the carriage on the basis of the predicted time, wherein the printing head is driven based on the position generation signal to perform printing even in a region where the carriage is accelerated/decelerated.
The third object is attained by a movement control method according to the third aspect of the present invention for controlling movement of a member to be driven by using a scale having a plurality of indices at a predetermined interval, and a sensor which is attached to the member to be driven along the scale and detects the indices, comprising the steps of predicting, on the basis of an output waveform of the sensor, a time until a next index is detected, and generating a signal concerning a current position of the member on the basis of the predicted time.
More specifically, according to the present invention, to control movement of a member to be driven by using a scale having a plurality of indices at a predetermined interval, and a sensor which is attached to the member to be driven along the scale and detects the indices, a time until the next index is detected is predicted on the basis of the output waveform of the sensor. Then, a signal concerning the current position of the member is generated on the basis of the predicted time.
The time until the next index is detected can be almost accurately predicted from the output waveform of the sensor along with detection of a scale index. This prediction can provide information about the current position of the member to be driven with a precision several times the interval of the scale index.
The position of the member which is being accelerated/decelerated can be controlled with high precision without setting a very small interval of the scale index.
Applying the present invention to a printing apparatus achieves high-quality printing even during acceleration/deceleration. The time during which no printing is done can be shortened to increase the printing speed. The length (width) of the printing apparatus in the scanning direction can be shortened to downsize the whole apparatus.
The position signal generation means preferably includes interpolation means for adding an interpolation signal every predetermined time interval within the time.
The prediction means preferably predicts the time by predetermined calculation using time intervals at which a plurality of indices are detected.
The sensor preferably detects the indices in a non-contact manner.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.